In cell phones, liquid-crystal TV's, and the like, the number of products having an illuminance sensor for regulating screen brightness has been increasing in recent years. Such an illuminance sensor is required to have the same sensitivity as the human eye. However, there is the following problem. The optical semiconductor element employed is sensitive not only to the visible rays but also to near infrared rays through a wavelength range of about 900 to 1,100 nm. Therefore, the optical semiconductor element, when used in its original state, senses near infrared rays, which are not sensible by human beings, and the sensor judges the environment “bright”. For preventing such a problem concerning the illuminance sensor, it is necessary to use an optical filter or the like to prevent the optical semiconductor element from being sensitive to near infrared rays. On the other hand, an epoxy resin composition excellent in heat resistance, impact resistance, transparency, etc. has come to be commercially used as an encapsulating material for optical semiconductors. In producing an illuminance sensor such as that described above, there has been employed a technique in which the upper side of an optical semiconductor element is coated, for example, with an optical filter material having the function of shielding near infrared rays and this optical semiconductor element having the optical filter formed thereon is encapsulated with an epoxy resin composition which is transparent in the visible light region and near infrared region.
In the technical field of such illuminance sensors, there presently is an earnest desire for imparting the optical filtrating function to an epoxy resin itself to be used as an encapsulating resin, for the purposes of eliminating or reducing the step/cost of separately forming an optical filter on the upper surface of an optical semiconductor element and of imparting the function of shielding near infrared rays to the side surfaces of the optical semiconductor element.
On the other hand, besides the use of an optical filter such as that described above, the following techniques of using a material having the function of shielding near infrared rays may be used for imparting the optical filtrating function to an illuminance sensor. For example, a heat-ray-cutting laminated glass for automotive and other uses (see, JP-A-2005-187226), a near-infrared-cutting film used in, e.g., plasma display panels (PDPs), and the like may be applied.
However, the heat-ray-cutting laminated glass used in motor vehicles and other applications has a drawback that a compound which mainly absorbs or reflects middle infrared rays is contained in, e.g., the interlayer of the laminated glass and, hence, this glass is low in the ability to shield near infrared rays and is insufficient for use in the illuminance sensor application in which the invention is intended to be used.
The near-infrared-cutting film used in PDPs and the like is produced by dissolving a colorant absorbing near infrared rays having wavelengths of 800 or 900 nm or longer in poly(ethylene terephthalate) (PET), poly(methyl methacrylate) (PMMA), or the like and then forming this polymer into a film. Consequently, one of the properties required to the colorant is solubility in organic solvents, and dyes such as diimonium salts (see, JP-A-2004-182857) and cyanine colorants (see, JP-A-2004-315789) are used as the colorants for PDPs and the like.
However, the thermal stability of those colorants is about 100° C. at the most because of the steps for producing the near-infrared-cutting film for use in PDPs and for producing the PDPs and because of the environment in which the PDPs are used. That temperature is considerably lower than the curing temperature of resins for optical-semiconductor encapsulation, which should be about 120 to 170° C. Consequently, when a colorant used in PDPs or the like is used, this colorant undergoes alteration such as pyrolysis, due to the action of an acid or basic compound used in raw materials for the resin and due to heating in the step of curing the resin, whereby a problem, for example, that the colorant disadvantageously changes in the optical property of shielding near infrared rays occurs.